while 1:
    num = input("请输入成绩(0-100)(exit退出):")
    if num.isdigit():
        if int(num) > 100 or int(num) < 0:
            print("请输入0-100的数")
        elif 0 <= int(num) < 60:
            print("不及格")
        elif 60 <= int(num) < 85:
            print("良好")
        else:
            print("优秀")
    elif num == "exit":
        break
    else:
        print("请输入数字")



